The goal of this proposal is to develop novel methods for high-yield, low- cost production of high performance cerium-doped lutetium oxyorthosilicate (LSO) scintillating crystals. The motivation is that LSO is amongst the most promising new scintillators discovered in almost five decades, with a unique combination of important properties for x and gamma-ray spectroscopy, namely: high density, fast decay, and large light yield relative to BGO. LSO seems to be a prime candidate to replace BGO in PET systems. However, the practical utilization of LSO is hindered by difficulties related to crystal growth (Czochralski method) due to the high temperatures employed. During the Phase I effort we successfully concluded a feasibility study which validated the innovative approach using a new low-temperature crystal growth technology to produce scintillating LSO crystals. Light transparent polycrystalline LSO samples of a few mm3 in volume were grown and investigated for their material properties, scintillation properties and response to gamma-rays. The properties of the new crystals compared well with high-quality crystals grown by the Czochralski method. In Phase II we will optimize the growth technique and streamline the process to obtain large volume, high performance and low cost LSO scintillating crystals specifically suited for PET detector rings. Towards this goal we will also develop and implement novel casting techniques to directly produce rectangular crystals and blocks of crystals with the correct dimensions for current PET instruments. Finally we will set-up a preproduction line and evaluate yields and quality of the grown crystals using evaluation techniques established in Phase I. PROPOSED COMMERCIAL APPLICATIONS: To date LSO is still not commercially available. When available its use will be widespread in hosts of applications leading to immediate performance gains, or enabling completely new uses where fast-timing or high counting-rate is needed. These include: PET; high-energy physics; industrial process control; environmental monitoring; geophysics; and space instrumentation etc., as well as brand new uses with solid-state photodetectors such as APD's and new drift photodetectors.